Method of cation exchanging synthetic faujasite



Uited States Patent fifice 3,375,065 Patented Mar. 26, 1968 1 Claim.(Cl. 23-112) ABSTRACT OF THE DISCLOSURE Method of cation exchangingcrystalline zeolite aluminosilicates to reduce the sodium content,expressed as the oxide, of the zeolite to less than 1%. The process ischaracterized by a primary sequence comprising a cation exchange stepfollowed by a heat treatment step followed by another cation exchangestep. The sequence is applied either singly or multiply, depending uponthe particular materials, temperatures, cation exchange solu tionconcentrations, etc., used. In a further embodiment the second cationexchange solution contains desirable metal cations, such as rare earths.

This application is a continuation-in-part of application Ser. No.318,249, filed Oct. 23, 1963 and now abandoned, and application Ser. No.367,864, filed May 15, 1964. p

This invention relates to an improved method for replacing exchangeablecations in zeolitic materials with other exchangeable cations. Inparticular this invention relates to cation exchange processes forreplacing cations in zeolitic materials such as synthetic faujasites,for example, with greater exchange efficiency, to cation exchangeprocesses for making synthetic faujasites having a greater thermalstability, and to the thermally stable synthetic faujasite compositionsproduced thereby.

In summary, the process of this invention is a method of cation exchangeof crystalline zeolitic materials comprising the steps of contactingthezeolite with a solution containing exchangeable cations, separating thezeolite from the solution and heating up to a temperature above 350 F.but which is insufficient to cause significant changes in the crystalstructure of the zeolite, and contacting the zeolite with a solutioncontaining exchangeable cations, whereby substitution of exchangeablecations in the zeolite is greatly facilitated.

In summary, the process of this invention for producing a syntheticfaujasite having an improved thermal stability comprises contacting anammonium cation exchanged synthetic fajasite containing less than oneweight percent alkali metal cations, expressed as the oxide, with anaqueous solution containing stabilizing cations selected from the groupconsisting of magnesium, rare earths, and mixtures thereof, andrecovering the thermally stable faujasite product. i

In summary, the composition of this invention cornprises ammonium cationexchanged .synthetic faujasite having a silica to alumina ratio withinthe range of from 3.5 to 7, an alkali metal cation content expressed asthe oxide of less than one weight percent, and a rare earth cationcontent expressed as the oxide of from 5 to 25 Weight percent.

One particular preferred embodiment of the process of this inventionwhich employs the improved ion exchange technique comprises theformulation of a thermally stable synthetic faujasite and includes thesteps of contacting the faujasite .with an anqueous solution containingammonium ions, separating the ammonium exchanged faujasite from thesolution, heating the faujasite up to a temperature above 350 F. butwhich is insuificient to cause significant changes in the crystalstructure of the zeolite, contacting the faujasite with an aqueoussolution containing ammonium ions, and contacting the faujasite with anaqueous solution containing exchangeable stabilizing cations selectedfrom the group consisting of magnesium, rare earth cations, and mixturesthereof, whereby a thermally stable faujasite is formed.

Substitution of exchangeable cations in crystalline zeolites is oftennecessary in order to obtain zeolites which are particularly suitablefor specialized commercial uses. Replacement of cations with othercations to vary the pore size of crystalline zeolites in order toseparate moleculesby selective adsorption with the zeolites is oftenfound to be desirable. In addition, removal of objectionable cations,and the replacement thereof with beneficial cations is usually requiredto produce active, selective, and thermally stable hydrocarbonconversion catalysts from zeolites as they are found in nature orsynthesized.

Prior to the method of this inventiornbase exchange of zeolites was alengthy, expensive process. In order to obtain replacement of amajorproportion of a cation in a zeolite with another cation, theexchange sequence, comprising solution and separation of the zeolitetherefrom, had to be repeated many times. Typical examples of themagnitude of this technical difiiculty are illustrated in the summaryTable VII of vU.S. Patent No. 3,140,249. Example 16 of that table showsthat eight separate exchanges were required to lower the sodium level to1.09 weight percent by exchange with an ammonium chloride solution.Other examples in the tables with other cations show the necessity formany separate exchanges to obtain replacement of a major proportion ofthe exchangeable cations in the zeolite with other cations.

It is one object of this invention to provide an improved method forreplacement of exchangeable cations in zeolites with other cations bybase exchange whereby the number of exchanges required is greatlydiminished.

It is another object of this invention to provide a method for producinga thermally stable zeolite by base exchange techniques and the productof this process.

A principal feature of the vprocess of this invention comprisesthermally treating crystalline zeolites between base exchangeoperations.

Any crystalline zeolite having cations which can be replaced by baseexchange techniques can be employed in the process of this invention.Examples of suitable synthetic zeolites are showrrin Table A.

TABLE A Oxide Mole Ratios (shown as alkali metal oxide form) PatentDisclosure wooov-wor- $0.2 Nalomuomasgrs SiOgzO-(S H1O... 510.05Na1O:AlzOs:2.2=l;0.05 sionxulo .UiCLl KnO:AlzOs:2.0:i:0.1 sionxrno..-

Zeolite KG .I

.9-L1 N320 :AlaOa:2.3-4.2 SlOgtZfi-Lfi H2O eeeees eee ee.

Among the naturally occurring crystalline aluminosilicates which can beemployed in the process of this invention are included levynite,dachiardite, erionite, faujasite, analcite, paulingite, noselite,ferriorite, heulandite, scolecite, stibite, clinoptilolite, harmotome,phillipsite, 'brewsterite, flakite, datolite, and aluminosilicatesrepresented as follows:

Chabazite, N21 O.Al O .4SiO .6l-l O Gmelinite, Na O.Al O .4SiO .6I-I OCancrimte, 3 (Na O.Al O .2SiO .Na CO Leuci te,

Lazurite, (Na, Ca) Al Si O 4.2(S, C], 50,) Scaplite, N214Al3Si9024.cl

Mesolite, .Na O.Al O .3SiO .2-3I-I O Ptilolite, Na O.Al O lSiO .4H OMordenite, Na O.Al O .10SiO .6.6H O Nepheline, Na O.Al- O .2SiO

Natrolite, Na O.Al O .3SiO .2H O Sodalite, 3 (Na O.Al O .2SiO .ZNaClCertain embodiments of the process of this invention relate to thermallystable synthetic faujasites. Synthetic faujasites are defined asincluding both Type X and Type Y zeolites, examples of which aredisclosed in US. Patent Nos. 2,882,244 and 3,130,007, respectively.

The cations which can be employed in the process of this inventioninclude hydrogen, exchangeable cations which decompose on heating toprovide hydrogen ions, and metals in Groups I-A through VIII of thePeriodic Table. A wide variety of acidic compounds can be employed withfacility as a source of hydrogen ions and include both inorganic andorganic acids. The acid concentration in the exchange solution can varyover a wide range, not being sufiicient to destroy the crystallinestructure of the particular zeolite employed. The pH ranges suitablevary from zeolite to zeolite. For example, the pH of the exchangesolution should be above 4 when the zeolite contacted therewith isfaujasite. Other zeolites such as mordenite can tolerate an even lowersolution pH.

Representative inorganic acids which can be employed include acids suchas hydrochloric acid, hypochlorous acid, chloroplatinic acid, sulfuricacid, sulfurous acid, hydrosulfuric acid, peroxydisulfonic acid (H S Operoxymonosulfuric acid (H 80 dithionic acid (P1 8 0 sulfamic acid (HNHS H), amidodisulfonic acid (NH(SO H) chlorosulfuric acid, thiocyanicacid, hyposulfurous acid (P1 8 0 pyrosulfuric acid thiosulfuric acid (HS O nitrosulfonic acid (HSO NO) hydroxylamine disulfonic acid ((HSONOH), nitric acid, nitrous acid, hyponitrous acid, carbonic acid and thelike.

Typical organic acids which find utility in the practice of theinvention include the monocarboxylic, dicarboxylic and polycarboxylicacids which can be aliphatic, aromatic or cycloaliphatic in nature.

Representative aliphatic monocarboxylic, dicarboxylic and polycarboxylicacids include the saturated and unsaturated, substituted andunsubstituted acids such as formic acid, acetic acid, chloroacetic acid,dichloroacetic acid, trichloroacetic acids, bromoacetic acid, propionicacid, Z-bromopropionic acid, 3-bromopropionic acid, lactic acid,n-butyric acid, and isobutyric acid, crotonic acid, n-valeric acid,isovaleric acid, n-caproic acid, cenanthic acid, pelargonic acid, capricacid, undccylic acid, lauric acid, myristic acid, palmitic acid, stearicacid, oxalic acid, malonic acid, succinic acid, glutaricacid, adipicacid, pimelic acid, suberic acid, azelaic acid, sebacic acid,alkyl-succinic acid, alkenylsuccinic acid, maleic acid, fumaric acid,itaconic acid, citraconic acid, mesaconic acid, glutonic acid, muconicacid, ethylidene malonic acid, isopropylidene malonic acid, allylmalonic acid.

Representative aromatic and cycloaliphatic moncarboxylic, dicarboxylicand polycarboxylic acids include 1,2-cyclohexanedicarboxylic acid,1,4-cyclohexanedicarboxylic acid, Z-carboxy-2-methylcyclohexaneaceticacid, phthalic acid, isophthalic acid, terephthalic acid, 1,8-naphthalenedicarboxylic acid, 1,2-naphthalenedicarboxylic acid,tetrahydrophthalic acid, S-carboxycinnamic acid, hydrocinnamic acid,pyrogallic acid, benzoic acid, ortho-, metaand paramethyl, hydroxy,chloro, bromo and nitrosubstituted benzoic acids, phenylacetid acid,mandelic acid, benzylic acid, hippuric acid, benzenesulfonic acid,toluenesulfonic acid, met-hancsulfonic acid and the like.

Other sources of hydrogen ions include carboxy polyesters prepared bythe reaction of an excess polycarboxylic acid or and anhydride thereofand a polyhydric alcohol to provide pendant carboxyl groups.

Still other materials capable of providing hydrogen ions are ionexchange resins having exchangeable hydrogen ions attached to baseresins comprising cross-linked resinous polymers of monovinyl aromaticmonomers and polyvinyl compounds. These resins are well known materialswhich are generally prepared by co-polymerizing in the presence of apolymerization catalyst one or more monovinyl aromatic compounds, suchas styrene, vinyl toluene, vinyl xylene, with one or more divinylaromatic compounds such as divinyl benzene, divinyl toluene,

divinyl xylene, divinyl naphthalene and divinyl acetylene.

Following copolymerization, the resins are further treated with suitableacids to provide the hydrogen form of the resin.

Still another class of compounds which can be employed are ammoniumcompounds which decompose to provide hydrogen ions when analuminosilicate treated with a solution of said ammonium compound issubjected to temperatures below the decomposition temperature of thealuminosilicate.

Representative ammonium compounds which can be employed include ammoniumchloride, ammonium bromide, ammonium iodide, ammonium carbonate,ammonium bicarbonate, ammonium sulfate, ammonium sulfide, ammoniumthiocyanate, ammonium dithiocarbamate, ammonium peroxysulfate, ammoniumacetate, ammonium tungstate, ammonium hydroxide, ammonium molybdate,ammonium benzoate, ammonium borate, ammonium carbamate, ammoniumsesquicarbonate, ammonium chloroplumbate, ammonium citrate, ammoniumdithionate, ammonium fluoride, ammonium gallate, ammonium nitrate,ammonium nitrite, ammonium formate, ammonium propionate, ammoniumbutyrate, ammonium valerate, ammonium lactate, ammonium malonate,ammonium oxalate, ammonium palmitate, ammonium tartrate and the like.Still other ammonium compounds which can be employed include tetraalkyland tetraaryl ammonium salts such as tetramethylammonium hydroxide,trimethylammonium hydroxide. Other compounds which can be employed arenitrogen bases such as the salts of guanidine, pyridine, quinoline, etc.

A wide variety of metallic compounds can be employed with facility as asource of metallic cations and include both inorganic and organic saltsof the exchangeable metals of Group I-A through Group VIII of thePeriodic Table.

Representative of the salts which can be employed include chlorides,bromides, iodides, carbonates, bicarbonates, sulfates, sulfides,thiocyanates, dithiocarbamates, peroxysulfates, acetates, benzoates,citrates, fluorides, nitrates, nitrites, formates, propionates,butyrates, valerates,'lactates, malonates, oxalates, palmitates,hydroxides, tartrates and the like. The only limitations on theparticular metal salt or salts employed are that it be soluble in thefluid medium in which it is used. The preferred salts are the chlorides,nitrates, acetates and sulfates.

Of particular interest are stabilizing cations, i.e., cations whosepresence in the zeolite tends to increase the thermal stability of thezeolite. These ions include magnesium and the rare earths. Salts of rareearth metals including cerium, lanthanum, praseodymium, neodymium,illinium, samarium, europium, gadolinium, terbium, dysprosium, holmium,erbium, thulium, yttrium, ytterbium and lutecium may be employed.

The rare earth salts employed can either be the salt of a single metalor preferably, of mixtures of metals such as a rare earth chloride ordidymium chlorides. As hereinafter referred to, a rare earth chloridesolution is a mixture of rare earth chlorides consisting essentially ofthe chlorides of lanthanum, cerium, neodymium and praseodymium withminor amounts of samarium, gadolinium and yttrium. The rare earthchloride solution is commercially available and it contains thechlorides of a rare earth mixture having the relative composition cerium(as CeO 48 percent by weight, lanthanum (as La O 24 percent by weight,praseodymiu'm (as Pr O 5 percent by weight, neodymium (as Nd O 17percent by weight, samarium (as Sm O 3 percent by weight, gadolinium (asGd O 2 percent by weight, yttrium (as Y O 0.2 percent by weight andother rare earth oxides 0.8 percent by weight. Didymium chloride is alsoa mixture of rare earth chlorides, but having a low cerium content. Itconsists of the following rare earths determined as oxides: lanthanum,4546 percent by weight; cerium 1-2 percent by weight; praseodymium, 9-10percent by weight; neodymium, 3233 percent by weight; samarium, 5-6percent by weight; gadolinium 3-4 percent by weight; yttrium 0.4 percentby weight; other rare earths 1-2 percent by weight. It is to beunderstood that other mixtures of rare earths are equally applicable inthe instant invention.

Representative metal salts which can be employed, aside from themixtures mentioned above, include silver sulfate, silver nitrate, silveracetate, silver arsenate, silver citrate, silver carbonate, silveroxide, silver tartrate, calcium acetate, calcium arsenate, calciumbenzoate, calcium bromide, calcium carbonate, calcium chloride, calciumcitrate, beryllium bromide, beryllium carbonate, beryllium hydroxide,beryllium sulfate, barium acetate, barium bromide, barium carbonate,barium citrate, barium malonate, barium nitrite, barium oxide, bariumsulfide, lithium chloride, sodium chloride, sodium sulfate, sodiumnitrate, potassium chloride, potassium sulfate, potassium nitrate,magnesium chloride, magnesium bromide, magnesium sulfate, magnesiumsulfide, magnesium acetate, magnesium formate, magnesium stearate,magnesium tartrate, zinc sulfate, zinc nitrate, zinc acetate, zincchloride, zinc bromide, aluminum chloride, aluminum bromide, aluminumacetate, aluminum citrate, aluminum nitrate, aluminum oxide, aluminumphosphate, aluminum sulfate, titanium bromide, titanium chloride,titanium nitrate, titanium sulfate, zirconium chloride, zirconiumnitrate, zirconium sulfate, chromic acetate, chromic chloride, chromicnitrate, chromic sulfate, ferric chloride, ferric bromide, ferricacetate, ferrous chloride, ferrous arsenate, ferrous lactate, ferroussulfate, nickel chloride, nickel bromide, cerous acetate, cerousbromide, cerous carbonate, cerous chloride, cerous iodide, ceroussulfate, cerous sulfide, lanthanum chloride, lanthanum bromide,lanthanum nitrate, lanthanum sulfate, lanthanum sulfide, yttriumbromate, yttrium bromide, yttrium chloride, yttrium nitrate, yttriumsulfate, samarium acetate, samarium chloride, samarium bromide, samariumsulfate, neodymium chloride, neodymium oxide, neodymium sulfide,neodymium sulfate, praseodymium chloride, praseodymium bromide,praseodymium sulfate, praseodymium sulfide, etc.

The base exchange steps of the process of this invention are carried outby conventional techniques. In general, the zeolite to be exchanged iscontacted with a liquid medium containing the exchangeable cationsdissolved therein. The zeolite undergoes rapid exchange, but prolongedcontact is normally advantageous for efficient operation. The speed ofthe base exchange is largely dependent upon the solution temperature,the higher solution temperatures providing a more rapid exchange.Solution temperatures within the range of from 60 to 220 F. arepreferred. At these temperatures, contact of the zeolite with theexchange solution for greater than about 0.1 hour is usually sufficient.Longer contact times can be employed but the effective exchange obtaineddiminishes with the time of contact.

The liquid medium can be any liquid in which the exchangeable cation issoluble and which does not destroy the zeolite being exchanged. Polarliquids are generally preferred such as alcohols and water, for example.Water is the liquid generally employed in commercial base exchangeprocesses, and the following descriptions will relate to base exchangein aqueous solutions. However, it should be realized that other liquidsare also operable in the process of this invention as the exchangemedia.

The concentration of exchangeable cations which can be employed in theexchange solution can vary widely, depending upon the cation to bereplaced in the zeolite and the cation to be substituted therefor. Ingeneral, when the cation to be substituted has less affinity for thezeolite than the cation to be replaced, higher cation concentration inthe exchange solution must be employed. The general requirements of theexchange solution concentration is a matter well understood in the ionexchange art.

It is known that with a particular zeolite to be exchanged and with agiven exchange solution, a certain limited proportion of the cation tobe replaced can be actually replaced in a single exchange step. Althoughthis limit can be varied somewhat by the solution concentration, theproportion of exchange obtained is often insuflicient to provide theproduct desired, As a result, many successive exchange steps arecommonly employed in the industry to obtain the desired degree ofsubstitution of a particular cation or cations into the zeolite. Witheach step, a smaller proportion of the desired cations can besubstituted into the zeolite.

By means of a process of this invention, the proportion of cationsreplaced in the zeolite in the subsequent exchanges can be greatlyincreased, providing the degree of exchange desired in two exchangesteps rather than seven or more in some instances.

This highly beneficial improvement is obtained by heating the zeolite upto a temperature of above 350 F. and preferably above 500 F. but whichis insufficient to change the crystal structure of the zeolite betweensuccessive cation exchange steps. In general, the higher temperatureswithin this range provide the greatest increase in cations exchanged inthe following exchange step. The necessary heating can be obtained byany conventional technique such as a rotary furnace or simple oven. Theheating can also be obtained by spray drying the zeolites in a gasmedium having a temperature above 400 F. and preferably 550 F. to afinal moisture content of less than 30 weight percent.

Thermally stable zeolites can be prepared by a process of thisinvention. Synthetic faujasites containing less than one weight percentalkali metal cations, expressed as the oxide, which have been exchangedby contact with an aqueous solution containing ammonium ions can becontacted with an aqueous solution containing stabilizing cations suchas magnesium, rare earths and mixtures thereof. The alkali metal contentof the synthetic faujasite is preferably less than 0.5 weight percentexpressed as the oxide. Any concentration of dissolved rare earthchlorides can be present in the exchange solution since the rare earthions are preferentially removed from the solution. However, a practicalminimum concentration is 0.1 weight percent rare earth chloride since atlower concentrations, it becomes necessary to handle impractically largequantities of the exchange solution in order to introduce the desiredquantity of rare earth ions into the zeolite. The thermally stableproduct is a superior zeolite promoter for hydrocarbon conversioncatalysts.

The process of this invention is highly beneficial in reducing thenumber of exchange steps required to produce the desired ammoniumexchanged synthetic faujasite employed in this process. The followingprocedure can be employed, for example. A crystalline zeolite in thealkali metal form, for example synthetic sodium faujasite, is placed inan aqueous solution containing from 1 to 20 weight percent ammoniumsulfate. The solution is maintained at a temperature of from 160 to 220F., and the contact of the zeolite with the solution is maintained forat least 0.1 hour. The zeolite is then separated from the soltuion andis heated up to a temperature above 350 F. but which is insufiicient tochange the crystal structure of the zeolite. The maximum allowabletemperature is dependent upon the amount of alkali metal remaining inthe zeolite after the exchange, i.e., the lower the alkali metal contentof the zeolite, the higher the heating temperature which can be employedwithout damaging the crystal structure of the zeolite. After thisheating step the faujasite may be contacted with a solution containingfrom 1 to 20 weight percent of an ammonium salt and having a temperaturewithin the range of from about 160 to 220 F. for at least 0.1 hourwhereby ammonium ions are substituted for a portion of the exchangeablecations in the faujasite. The solutions containing the ammonium ions maycontain stabilizing cations selected from the group consisting ofmagnesium, rare earths, and mixtures thereof whereby a portion of thestabilizing ions are introduced into the faujasite.

Other aspects of the process of this invention are illustrated by thefollowing specific, but non-limiting examples.

Example 1 This example illustrates the normal difficulty encountered inthe removal of sodium from synthetic faujasite by usual ion-exchangetechniques.

A 300 g. sample of wet synthetic faujasite (about 150 g. dry basis) wastreated with 1000 g. of an aqueous 3% by weight ammonium sulfatesolution at C. for 15 minutes. The faujasite was then separated from thesolution and analyzed for sodium as Na O. The faujasite was thenreturned to a fresh aqueous solution of 3 percent ammonium sulfate andtreated as before. This process was repeated for a total of tenexchanges. The Na O content after each exchange is shown in Table A. Itcan be readily seen that the sodium content is reduced to about 3 weightpercent with the 3 percent solution but can be reduced to lower levelsonly with great difiiculty.

This example shows the unobvious increases in exchange efiicien-cyobtained with the process of this invention.

A 50 g. sample of wet synthetic faujasite (about 25 g. dry basis) wascontacted with 800 ml. of an aqeuous 5 weight percent ammonium sulfatesolution at C. for 15 minutes. This step was then repeated with a freshammonium sulfate solution. The sample was washed free of sulfate ionsand was then divided into two portions, Sample A and Sample B. Sample Awas heated to 1000 F. for one hour. Sample B was not heated. Each of thesamples was then subjected to a third exchange step as described above,and the samples were analyzed for sodium as Na O. The results are shownin Table B.

TABLE B Na o content, weight percent Sample After second exchange Afterthird exchange Example 3 This example shows the utility of the processof this invention in removing sodium cations from cha-bazite by ionexchange.

A 50 g. sample of natural chabazite was exchanged in TAB LE N 2120content, weight percent Sample After second exchange After thirdexchange As can be seen, the sodium content of Sample B was twice thatof Sample A, showing the utility of the process of this invention forexchanging zeolites other than faujasites.

Example 4 This example illustrates the unique advantages obtained withthe process of this invention using magnesium ions in the exchangesolution.

A 50 g. sample of wet synthetic faujasite (about 25 g. dry basis) wascontacted with 800 ml. of an aqueous 5 weight percent magnesium sulfatesolution at 100 F. for 15 minutes. This step was repeated with a freshmagnesium sulfate solution and the sample was washed free of sulfateions. The sample was divided into two portions, Samples A and B, andSample A was heated to 1000 F. for one hour. Each of the samples wasthen subjected toa third exchange step as described above, and thesamples were analyzed for sodium as Na O. The results are shown in TableD.

As shown in Table D, a substantial sodium exchange with magnesium ionstook place in the third exchange. In contrast, the sodium content ofSample B was hardly changed in the third exchange.

Example 5 This example shows the process of this invention producing athermally stable faujasite.

The synthetic faujasite employed in this example had the followingchemical composition on a dry basis, expressed in terms of mole ratiosof oxides:

A 4 pound sample of thissynthetic faujasite was contacted with asolution containing 8 pounds of ammonium sulfate in 24 pounds of waterfor one hour at 90 C. The exchange was repeated with a fresh solution asdescribed above, and was washed free of sulfate ions. The sample wasthen heated to 1000" F. for 3 hours. The sodium content of the zeoliteat this point was 2.94 weight percent Na O. The ammonium sulfateexdhange was then re peated 3 more times as above. The zeolite waswashed free of sulfate ions. The sodium content of the zeolite at thispoint was less than 0.5 weight percent Na O.

The zeolite was then contacted with the rare earth chloride solutionpreviously described containing 3 pounds of rare earth chloride in 50pounds of water at 100 F. for 15 minutes. The zeolite was then washedfree of chlofor ride ions, and was tested .for sodium and rare earthcontents and thermal stability. The sodium content was 0.42 weightpercent Na O, and the rare earth content, expressed as Re O was 13.47weight percent. The thermal stability of the zeolite was determined byheating individual samples for 2 hours, each sample being heated at adifferent temperature, and measuring the surface area of the products.The results are shown in Table E.

TABLE E TreatmentI-Ieating temperature, F. Surface area, m. /g. 1500 815A portion of the product was steamed at 1525 F. for 16 hours, and wasfound to have a surface area of 656 m. /g. after the treatment.

As can be seen above, the product of this invention exhibits aremarkable thermal stability and therefore has a superior utility foruse as a promoter in hydrocarbon conversion catalysts.

Example 6 This example shows the process of this invention for making asynthetic faujasite having unusual thermal stability.

The synthetic faujasite employed had a silica to alumina mole ratio ofapproximately 5. An ammonium cation exchanged form of this syntheticfaujasite having a sodium content of 0.19 weight percent Na O wascontacted with the previously described rare earth chloride solutioncontaining 10 g. of rare earth chloride in 500 ml. of water for 15minutes at C. The thermal stability of the product was determined byheating individual samples at different temperatures for 2 hours, andmeasuring the surface area of the products. The results are shown inTable F.

The product was analyzed and found to have a rare earth content of 18.6weight percent Re O (dry basis).

The unusual thermal stability of this product can be appreciated whenthe surface areas shown in Table F are compared with those shown inTable E. Even though the surface area of the product of this example islower after heating at 1500 F., it is much higher than the othermaterial after heating at 1700 F.

Obviously, many modifications and variations of the invention as hereinset forth may be made without departing from the essence thereof andonly such limitations should be applied as are indicated in the appendedclaim.

We claim:

1. A cation exchange method of producing a thermally stable syntheticcrystalline faujasite containing less than one weight percent alkalimetal, expressed as the oxide, which comprises:

(a) contacting a synthetic crystalline faujasite with an aqueoussolution containing ammonium cations, maintained at a temperature offrom to 220 F. for at least 0.1 hour,

(b) separating the crystalline :faujasite from the solution and heatingit at a temperature above 350 F. but which is insufiicient to causesignificant changes in the crystal structure of the faujasite,

(c) contacting the heated faujasi'te with an aqueous solution containingammonium cations, maintained at a temperature of from 160 to 220 F. forat least 0.1 hour whereby a crystalline faujasite containing ammoniumions and containing less than one weight percent alkali metal, expressedas the oxide, is formed, and

(d) recovering the faujasite of step (c) and contacting the so recoveredfaujasite with an aqueous solution containing exchangeable stabilizingcations selected from the group consisting of magnesium, rare earths,and mixtures thereof, whereby a thermally stable References Cited UNITEDSTATES PATENTS Rabo et a1. 23110 Frilette et a1. 252455 X Rabo et al.208ll1 Maher et al. 23-111 X faujasite is formed by ion exchangereplacement of 10 EDWARD J MEROS Primary Examiner ammonium ions withstabilizing cations.

